Such elements are known for example from DE-A3842702 or DE-A4439429. The described analytical elements contain the necessary reagents to carry out immunoenzymometric or immunoenzymometric-like methods of determination. In particular these are analyte or analyte analogue immobilized in a zone, between the sample application zone and detection zone and a conjugate composed of a bioaffine binding partner capable of a specific binding reaction with the analyte to be determined and a detectable label.
In the case of DE-A 3842702 an enzyme label is described as the detectable label. In order to make this label visible it is necessary to contact it with a chromogenic enzyme substrate such that a colour is formed as a result of the enzymatic activity. The requirement that the label has to be made visible is a complication, costly due to the measures that have to be taken and furthermore may result in technical difficulties for example when the corresponding enzyme substrate has stability problems in the analytical element.
Therefore recently direct labels have been preferred as described in DE-A 4439429. These direct labels are for example metal or latex particles which have an intrinsic colour and can be visualized with the naked eye. Nowadays a gold label is particularly preferred. For this an appropriately labelled bioaffine binding partner depending on the analyte is prepared for which optimal conditions then have to be created on the analytical element for reaction and storage. This individual adaptation to the analyte to be determined is very laborious. Depending on the analyte to be determined, the required polyclonal or monoclonal antibodies can behave very differently when conjugated to gold particles. This can lead to different stabilities of gold conjugates. The differences in the behaviour of the various polyclonal antibodies or various monoclonal antibodies when coated on gold particles can result in quite different spatial arrangements of the antibodies on the gold particles which leads to steric problems when such conjugates are reacted with the analyte and can thus result in a poor sensitivity.